Electrical and electronic equipment and components are designed to operate effectively within a specified range of voltages. Disturbances in an electrical system can create voltage surges which adversely affect the operation of electrical equipment. Such voltage surges can damage sensitive components or produce noise or other undesirable characteristics in an electrical device. Accordingly, it will be appreciated that it would be highly desirable to protect sensitive equipment from voltage surges so that the equipment operates without damage or interruption.
Modern telephones, modems, and other electronic devices that connect to telephone lines are susceptible to damage or faulty operation from voltage surges. A voltage surge can occur when lightning strikes a telephone line or when voltages are induced in the telephone line from nearby equipment such as motors and faulty electrical equipment.
A typical telephone line has a lightning arrestor to protect the inside telephone wiring and instruments from high voltage surges that occur when lightning stikes the telephone line. While such lightning arrestors are effective in preventing high voltage surges from reaching the internal wiring and instruments connected thereto, they are inadequate to protect the telephone instruments and inside wiring from the lower voltage power surges which are also capable of damaging electronic instruments. Accordingly, it will be appreciated that it would be highly desirable to provide low voltage surge protection for the telephone instrument and inside wiring.
Gas discharge surge suppressors are standard in many applications. However, the construction of conventional three-terminal gas discharge devices is such that the breakdown voltage between the tip and ring terminals is greater than the breakdown voltage between the tip and ground terminals and the breakdown voltage between the ring and ground terminals. Most of the devices normally connected to a telephone line can withstand significant tip-to-ground voltages and ring-to ground voltages but are frequently unable to survive the application of a large tip-to-ring voltage. Therefore, conventional three-terminal gas discharge devices do not provide the lower breakdown voltage between the terminals which are least able to withstand the higher voltage. Therefore, it is desirable to have a gas discharge surge suppressor which has a tip-to-ring breakdown voltage which is less than the tip-to-ground breakdown voltage and the ring-to-ground breakdown voltage.
Varistors, zeners, and other similar electronic devices provide surge protection but, because of the constant breakdown voltage of these devices, the internal heating caused by surge absorption can exceed their heat dissipation capability, especially with repeated surges.
Some surge protectors are bulky items unsuitable for location within or near the equipment it protects. Also, some surge protectors are not aesthetically pleasing. It is desirable to have a compact gas discharge surge suppressor for a telephone line that can be incorporated into telephone instruments, modems, and other devices that are connected to the line. It is also desirable to have a surge suppressor that can be added to existing telephone lines to provide protection from low level voltage surges.